1. Field of the Invention
The present invention relates to an apparatus for production of single crystal oxide films by liquid-phase epitaxy and, more particularly, to an apparatus for producing, by liquid phase epitaxy, single crystal oxide films such as magnetic garnet single crystal films suitable for use in magnetostatic-wave devices, and lithium niobate suitable for use in optical devices.
2. Description of the Prior Art
For production of single crystal oxide films by liquid phase epitaxy, there has been used an apparatus having a structure as shown in FIG. 2. This apparatus comprises a vertically arranged core tube 1 of alumina, resistance heaters 2a, 2b and 2c arranged around the core tube 1, a cylindrical furnace body or shell 3 of a heat-insulating material for covering the core tube 1, a shutter 4 for closing an opening of the core tube 1, a platinum crucible 6 for holding raw materials of oxide films, a support 7 for supporting the crucible 6, and a holder 9 of platinum or a platinum alloy connected to a rod 10 for holding a substrate 8 horizontally.
Using the apparatus, a single crystal oxide film, for example, a magnetic garnet film is produced in the following manner. Firstly, oxides of elements constituting a magnetic garnet, i.e., Fe.sub.2 O.sub.3 and Y.sub.2 O.sub.3, are charged into a platinum crucible 6 along with PbO and B.sub.2 O.sub.3 serving as a solvent. After the crucible 6 has been mounted on the support 7 in the core tube 1, the raw material in the crucible 6 is heated to and melted at 1200.degree. C. to prepare a homogenized melt 5. The resultant melt 5 is then cooled to a temperature between liquidus line and solidus line, i.e., about 900.degree. C. and kept at that temperature to convert the melt into a supercooled state.
Then, a substrate 8, generally made of Gd.sub.3 Ga.sub.5 O.sub.12 (hereinafter referred to as "GGG") and previously attached to the holder 9, is inserted into the core tube 1 by lowering the supporting rod 10 into the core tube 1 so that the substrate is pre-heated to the atmospheric temperature. After this, the substrate 8 is immersed into the melt 5 and rotated at a fixed level therein for a certain period of time while reversing the direction of rotation periodically. During this step, a single crystal film of magnetic garnet is epitaxially grown on the substrate. Finally, the substrate 8 is drawn up from the melt 5 and rotated above the melt 5 at a high rate of revolution to remove the melt adhered to the epitaxially grown magnetic garnet single crystal film.
In the apparatus of the prior art, however, the heat generated by the resistance heaters is initially consumed to raise the temperature of the core tube 1 and the raw materials in the crucible as they are heated by radiant heat emitted from the core tube. Thus, it takes a long time to prepare the homogenized melt because of the large heat capacity of the apparatus. Similarly, it takes a long time to cool the homogenized melt to the supercooled state because of the large heat capacity of the apparatus. For this reason, spontaneous nucleation takes place during cooling of the melt, causing precipitation of garnet in the melt, which in turn causes a lowering of quality of the single crystal film as the precipitate is taken into the single crystal film during epitaxial growth of the single crystal.